Stabilized phenolic resins

ABSTRACT

The addition of a water-absorbent, finely divided powder to a phenolic resole resin provides a stabilized resin composition which cures in the presence of an acid catalyst at ambient temperatures to a relatively thick coating having a reduced number of defects, e.g., pinholes and blistering. For example, a resole resin composition containing a stabilizing amount of fumed silica can be blended with a mixture of benzene sulfonyl cloride and trichloroacetic acid, applied to a substrate and cured to form an essentially defect-free coating.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of our previously filed applicationSer. No. 5,738, filed Jan 23, 1979 U.S. Pat. No. 4,235,762.

BACKGROUND OF THE INVENTION

This invention relates to phenolic resole resins, particularly tostabilized phenolic resole resin compositions and to the curedcompositions prepared therefrom.

Thermoset phenolic resins are known to exhibit excellent physicalproperties, e.g., strength and adhesion, and excellent chemicalproperties, such as resistance to attack by various solvents and acids.Due to these properties, phenolic resins are used extensively in coatingapplications, particularly as protective coatings for containers, airconditioning equipment, water tanks and the like.

It is well known in the art that the condensation reaction of analdehyde with a phenol provides materials curable to thermoset phenolicresins. Base-catalyzed condensation reactions of at least astoichiometric amount of an aldehyde with a phenol provide a condensateknown as a phenolic resole resin or A-stage resin. Alternatively, acidcatalyzed condensation of a phenol with less than a stoichiometricamount of aldehyde provides a phenolic novolak resin.Characteristically, phenolic resole resins can be heat cured to fullycross-linked, infusible resins (commonly referred to as C-stage resins)without the need for added cross-linking agent. From this standpoint,they are more descriptively referred to as one-step resins in contrastto phenolic novolaks (two-step resins) which require the addition of across-linking agent for curing.

Unfortunately, resole resins are unstable. Frequently, upon standing,this instability is evidenced by the formation of a distinct water richphase, which phase generally separates from the remainder of the resoleresin. Often, under normal storage and shipping conditions, thisinstability imparts to the resin undesirable handling characteristicsand renders the resin unusable.

Heretofore, several methods have been proposed for improving thestability of the resole resins. For example, it is known that reducingthe mole ratio of the reactants, i.e., moles of aldehyde per mole ofphenol, provides a more stable resin. See, for example, PolymerProcesses, edited by Calvin E. Schildknecht, published in 1956 byInterscience Publishers, Inc., New York, Chapter VIII. Unfortunately,the reduced aldehyde content in the resin increases the curingtemperature required to prepare the C-stage resin.

Alternatively, U.S. Pat. No. 1,802,390 discloses that maintaining theresole resin in an alcohol will increase the resin's stability.Unfortunately, the volatile material, i.e., the alcohol, promotes theformation of pinholes and similar defects in coatings preparedtherefrom.

Similarly, U.S. Pat. No. 2,937,159 teaches that the addition of a smallamount of certain aliphatic polyamines to the resole resin will increasethe stability thereof. Unfortunately, coatings and other products formedtherefrom exhibit a reduced resistance to chemical attack.

In view of the stated deficiencies of the prior art compositions, itremains highly desirable to furnish a stabilized phenolic resole resinwhich when applied to a suitable substrate will cure at relatively lowtemperatures to a chemically resistant coating substantially devoid ofimperfections.

SUMMARY OF THE INVENTION

Accordingly, one aspect of the present invention is a stabilizedphenolic resole resin composition comprising a phenolic resole resin andan amount of a finely divided, water-absorbent powder sufficient toreduce the amount of a distinct water rich phase formed in the resincomposition.

Another aspect of the present invention is a method of preparing acoating from said stabilized phenolic resole resin composition, saidmethod comprising the steps of (1) adding to the stabilized resincomposition a catalytic amount of an acid, (2) applying the catalyzedresole resin composition to a suitable substrate and (3)subjecting thecatalyzed resin composition to conditions sufficient to cure the resin.

Yet another aspect of the present invention is a normallywater-insoluble substrate coated with the cured, stabilized phenolicresole resin composition.

Surprisingly, the addition of the finely divided, water-absorbentmaterial to the phenolic resole resin reduces the formation of adistinct water rich phase therein. Moreover, upon the addition of anacid catalyst, the resole resin compositions of the present inventioncure at relatively low temperatures, with a room temperature cure beingeffective in many applications. Unexpectedly, upon cure, a coatingdevoid of imperfections is formed. By the term "coating devoid ofimperfections" is meant a coating which under visual inspection with nomagnification is essentially devoid of pinholes, holidays and othersimilar defects.

The stabilized phenolic resole resin compositions of this invention areuseful in coating and adhesive applications. Upon curing, the resincompositions form strong, durable coatings which are resistant tochemical attack by many chemicals such as strong acids, e.g.,hydrochloric acid, and various solvents, particularly chlorinatedsolvents.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of this invention, a phenolic resole resin is thereaction product of at least one phenol with at least one aldehyde, thealdehyde being employed in a molar excess with respect to the phenolic.

As the term is used herein, a "phenol" includes any phenolic compoundcapable of reacting with an aldehyde to form a resole resin,particularly those phenols employed heretofore in the preparation ofresole resins. Representative examples of such phenols include phenol(benzophenol); alkyl substituted phenols such as cresol, xylenol,cardanol, p-tert butylphenol and the like; phenylphenol; resorcinol andthe like. Combinations of such phenolic compounds are alsoadvantageously employed. Preferred phenols include phenol, resorcinol,2,4-xylenol and m-cresol; with phenol being especially preferred.

By the term "aldehyde" it is meant an aldehyde capable of reacting witha phenol, as hereinbefore described, to form a resole resin,particularly those aldehydes used heretofore in the preparation ofresole resins. Representative examples of such aldehydes includeformaldehyde (advantageously in the form of an aqueous solution such asformalin); formaldehyde yielding materials such as paraformaldehyde;acetaldehyde; furfural; butyraldehyde and the like. Preferred aldehydesare formaldehyde and paraformaldehyde, with formaldehyde beingespecially preferred.

The phenolic resole resin is prepared by reacting a molar excess of thealdehyde with the phenol in the presence of an effective amount of abase catalyst. Advantageously, the proportion of aldehyde to phenolbeing reacted is from about 1 to about 2.5, preferably from about 1.1 toabout 1.8, most preferably from about 1.3 to about 1.5, moles ofaldehyde per mole of phenol. Base catalysts advantageously employed andthe effective amounts of such catalysts are those which are commonlyemployed in the art. Typically, ammonia or a metal hydroxide such ascalcium hydroxide or sodium hydroxide are effectively employed as a basecatalyst, advantageously, at concentrations from about 2 to about 4weight percent based on the weight of the phenol. Methods for preparingresole resins are well known in the art and such conventional methodsare suitably employed in this invention. Illustrative of such methods ispresented in Polymer Processes, edited by Calvin E. Schildknecht,published in 1956 by Interscience Publishers, Inc., New York, ChapterVIII (pages 295-350).

The finely divided, water-absorbent powders useful in the practice ofthis invention include those materials which are insoluble in thephenolic resole resin and which (1) have a number average particle sizeof less than about 5000 A, preferably less than about 500 A, morepreferably less than about 200 A and (2) are capable of absorbing atleast about 1, preferably at least about 2, more preferably at leastabout 5, times their weight in water. For the purposes of thisinvention, the particle size of the powder is the primary particledimension of the particle as determined by conventional techniques suchas microscopic techniques similar to those disclosed by ASTM E 20-68.Water absorbance is also determined by conventional techniques, e.g.,comparing the weight of the dry powder with the weight of the wet powderafter the maximum amount of water has been absorbed thereby.

Of such materials, fumed powders such as fumed silicon dioxide, fumedtitanium dioxide and fumed aluminum oxide are preferred. Advantageously,such fumed powders have a number average particle size of less than 400A, preferably less than 200 A, when the particle size is determined fromthe surface area assuming the particles to be spherical in shape. Thesurface area is determined by the nitrogen adsorption method ofBrunauer, Emmett and Teller as disclosed in the Journal of the AmericanChemical Society, Vol. 60, published in 1938, page 309.

Methods for preparing such fumed inorganic powders are well known in theart and reference is made thereto for purposes of this invention. Aconventional method involves the flame-hydrolysis of a suitable gas,e.g., TiCl₄ or SiCl₄, by reacting the gas in a flame of hydrogen andoxygen to form the fumed inorganic plus hydrochloric acid.

In the practice of this invention, the finely divided powder is mixedwith the resole resin in an amount sufficient to reduce the amount of awater rich phase, which phase is distinct from the remainder of theresole resin composition. Such amount is also advantageously an amountwhich does not adversely and significantly affect the resin's physicaland chemical properties upon cure, e.g., does not promote the formationof pinholes, holidays and other imperfections in coatings preparedtherefrom. For the purposes of this invention, the amount of a distinctwater rich phase formed in the resin is presumed to be reduced, i.e.,the phenolic resole resin is presumed to be stabilized, when the amountof water or water rich material which forms a distinct phase, i.e., aphase which is visibly separate from the remainder of the resincomposition such as in a well defined layer or as a plurality ofdiscontinuous droplets in a continuous phase of the resin composition,is measurably reduced. By "measurably reduced" it is meant that suchwater or water rich phase is reduced by a measurable amount using testconditions hereinafter described.

Experimentally, the stabilizing effect of the finely divided, waterabsorbent powder on a resole resin is determined by the followingprocedure. The resole resin to be tested is prepared by conventionaltechniques. To a portion of the resin is blended the finely dividedpowder at its desired concentration. A second portion of the resoleresin remains neat, i.e., it contains no powder. Equal amounts by weightof each resin portion are subjected to extended storage in a closedcontainer at room temperature, e.g., 25° C., for an extended period oftime, e.g., 2-12 months. At the end of this storage period, each resinportion is examined for a water rich phase, which phase, if present,generally resides on the top of the remainder of the composition. Theamount of any water rich phase is measured by conventional techniques.For the purposes of this invention, the resin composition containing thefinely divided powder is presumed to be stabilized whenever the amountof the water rich phase is less than the amount of the water rich phasein the neat resole resin.

Advantageously, the finely divided powder is employed in an amountsufficient to reduce the amount of the water rich phase formed by atleast about 20, more preferably at least about 50, percent when theresole resin and stabilized resole resin composition are compared afterstorage for three months at 25° C. By way of example, a phenolic resoleresin which in neat form exhibits 5 g of a distinct water rich phase,has at least a 20 percent reduction in the amount of the water richphase formed, when an identical phenolic resole resin, when stabilized,exhibits a separate water rich phase of 4 g. Most preferably, thestabilized phenolic resole resin exhibits essentially no distinct waterrich phase.

The amount of the finely divided, water-absorbent powder mostadvantageously employed to stabilize the resin is dependent on manyfactors, including the specific phenol and aldehyde employed, theirrelative concentrations and the specific finely divided powder employed.Typically, the finely divided powder is advantageously employed atconcentrations from about 0.5 to about 5, preferably from about 0.7 toabout 2, weight percent, said weight percents being based on the totalweight of the resole resin. As a specific example, a resole resin whichis the reaction product of 1.4 moles of formaldehyde with 1 mole ofphenol is advantageously stabilized with from about 1 to about 1.5weight percent of a fumed inorganic powder based on the total weight ofphenolic resole resin. The most effective concentrations of the finelydivided powder are easily determined by experimental techniques as setforth herein.

In addition to the finely divided powder, it is often advantageous,although optional, to incorporate small amounts of a basic material intothe stabilized resole resin. Included within the term "basic material"are organic and inorganic bases, preferably those materials having apk_(b) greater than about 1.0 wherein pk_(b) is the dissociationconstant of the basic group in water at 25° C., and those materialswhich form such bases in the presence of water. Representative basicmaterials useful herein include the Group IIA metal hydroxides such asmagnesium hydroxide; the Group IIA metal oxides such as calcium oxide;certain transition metal oxides such as cadmium oxide and primary,secondary and tertiary amines, with tertiary amines such asbenzyldimethylamine, α-methylbenzyldimethylamine,dimethylaminomethylphenol and tridimethylaminomelthylphenol being thepreferred amines. When a basic material is employed, the stabilizedresin composition advantageously contains from about 0.05 to about 1.0,preferably from about 0.1 to about 0.25, weight percent of the basicmaterial, said weight percent being based on the weight of the resoleresin.

Optionally, the resole resin also contains various adjuncts such asfillers, lubricants, hardeners, stabilizers and the like. Adjunctsconventionally employed and their effects on the phenolic resins arewell known in the art. Reference is made thereto for the purpose of thisinvention. As an example of such art, reference is made to PolymerProcesses, edited by Calvin E. Schildknecht, published in 1956 byInterscience Publishers, Inc., New York, Chapter VIII.

Of the conventional adjuncts, a filler is advantageously employed formany applications, particularly in coating applications. By the term"filler" it is meant any essentially inert material used to stiffen,harden or thicken the resole resin composition or products preparedtherefrom and which reduce overall resin cost. Representative examplesof fillers suitably employed in this invention are graphite flakes;expanded clays, e.g., Al₂ O₃.3SiO₂.2H₂ O; calcium carbonate; barytes;silicates; glass spheres; slate flour; soft clays and the like. Althoughmany such conventional fillers possess excellent water absorbingproperties, their large size generally precludes their use as the finelydivided powder in this invention. However, if they are prepared in asize range sufficient to stabilize the phenolic resole resin asexemplified herein, the fillers can also be suitably employed as thefinely divided powder. Fillers which have been found especially usefulfor coating application are graphite flakes and expanded clay. Althoughthe concentration of the filler is not critical, concentrations fromabout 2 to about 20, preferably from about 3 to about 10, weight percentbased on the weight of the resole resin have been found to beadvantageous.

For many applications, a dispersing agent, i.e., a surface active agentwhich promotes uniform and maximum separation of fine solid particles,e.g., the fumed inorganic powder, is often advantageously employed. Thedispersing agents which are advantageously employed in this inventionare those which prevent the settling of the finely divided,water-absorbent powders, the optional fillers and other adjuncts whenthe resole resin is to stand for long periods prior to use, e.g., 6-12months. Of the conventional dispersing agents, anionic or nonionicpolymer type dispersing agents and mixtures thereof have been found tobe most advantageous in the practice of this invention. Representativeexamples of such dispersing agents are di-isobutylene-maleic anhydridesodium salt, polyacrylate or polymethacrylate salts, alkyl phenolpolyoxyethylene and the like. Di-isobutylene-maleic anhydride sodiumsalt is the most preferred. The concentration of the dispersing agentmost advantageously employed depends on many factors, including the typeand concentration of the resole resin, finely divided powder and fillersas well as the desired viscosity of the resin composition. Typically,concentrations of the dispersing agent from about 0.0001 to about 0.2,preferably from about 0.001 to about 0.1, weight percent based on thetotal parts by weight of the resole resin are advantageously employed.

Advantageously, the foregoing ingredients are employed in amounts suchthat upon mixing by the methods hereinafter described, a thixotropicmaterial, i.e., a gel-like material which when subjected to mildagitation behaves like a viscous liquid, results. For example, theingredients are advantageously employed in amounts sufficient to form agel-like material which will flow freely on application of slightpressure such as by brushing or rolling.

The finely divided, water-absorbent powder and optional adjuncts areblended with the resole resin using conventional techniques such as aroll mill, blender or the like. Preferably, the blending is by means ofa high speed mixer, e.g., a Dispersator, manufactured by the PremierMill Corp., operating at blade speeds in the range from about 5,000 toabout 20,000 rpm.

The stabilized resole resin composition can be cured to a normally solidmaterial using conventional techniques. The catalyst, times,temperatures and other curing conditions are well known in the art andusable in the practice of this invention. Reference is made thereto forthe purposes of this invention. Merely for the purposes of illustrationand not for limitation, reference is made to Organic Chemistry ofSynthetic High Polymers by Robert W. Lenz, published in 1968 byInterscience Publishers, Inc., New York, Chapter IV, "CarbonylAddition--Substitution Reactions," pages 113-138 and 140-142 and toPolymer Processes, edited by Calvin E. Schildknecht, published in 1956by Interscience Publishers, Inc., New York, Chapter VIII, "Condensationswith Formaldehyde" by T. J. Suen.

In many applications, particularly coating applications, curing isadvantageously carried out by adding to the stabilized resole resincomposition a catalytic amount of an acid and subjecting the catalyzedresin composition to conditions sufficient to cure the resin to anormally solid material. Acid catalysts advantageously employed arethose which, when employed in a catalytic amount, (1) will catalyze thecross-linking reaction of the resole resin and (2) do not coagulate theresin or cause the cured resin to exhibit catalyst strings, i.e., thosestring-like particles formed by the gelling of the resin. Representativeexamples of suitably employed acid catalysts include chlorinated acidssuch as mono-, di- or tri-chloroacetic acid; a salt of a weak base andstrong inorganic acid such as ammonium chloride, ammonium sulfate,ferric chloride and the like; maleic anhydride and the like. A catalyticamount of the acid is dependent upon many factors including the specificacid employed, the composition of the resole resin and the cure ratedesired. Typically, from about 0.1 to about 15, preferably from about0.2 to about 10, weight percent of the acid based on the weight of theresole resin is employed. At these concentrations, a cure temperaturefrom about 20° C. to about 100° C. is generally sufficient to cure thestabilized phenolic resole resin.

Advantageously, the acid catalyst is used in conjunction with an organicsulfonyl chloride, preferably benzene sulfonyl chloride; preferably as amixture of from about 5 to about 50 weight percent of the acid and fromabout 95 to about 50 weight percent of the organic sulfonyl chloride,said weight percents being based on the weight of the acid and sulfonylchloride.

In coating applications, the catalyzed, stabilized phenolic resole resincomposition of this invention is applied to a suitable substrate byconventional methods such as brushing, rolling, spraying or the like.Suitable substrates include normally water-insoluble materials such asmetals, glass or glass substitutes, or other like materials, thesurfaces of which having been advantageously primed with a suitableprimer, e.g., a cured epoxy or vinyl ester resin, and which are inert tothe catalyzed phenolic resole resin composition and the curedcomposition formed therefrom. Following its application, the catalyzedcomposition is cured to the substrate at conditions hereinbeforedescribed.

The following examples are set forth to illustrate the invention andshould not be construed to limit its scope. In the examples, all partsand percentages are by weight unless otherwise specified.

EXAMPLE 1

To a high speed mixer is added 222 g of a resole resin which is thereaction product of formaldehyde and phenol at a molar ratio of 1.4moles formaldehyde to 1 mole of phenol. To the resole resin is added 3 gof a fumed silica having a number average particle size of 120 A. Theresole resin and fumed silica are blended for about 5 minutes at a bladespeed of about 10,000 rpm. The resulting stabilized resole resincomposition (Sample No. 1) is poured into a 120 cc bottle, whic issubsequently capped, thereby making the bottle essentially impermeableto the passage of air.

In a similar manner, 222 g of an identical resole resin, except that itcontains no fumed inorganic powder, (Sample No. C) is prepared andpoured into a 120 cc bottle, which bottle is subsequently capped.

Each composition is stored in the capped bottle for a period of aboutthree months at a temperature of 22° C. At the end of this storageperiod, each container is inspected for a water rich phase. The resoleresin having the fumed inorganic powder added thereto, i.e., thestabilized resole resin composition is found to have essentially nodistinct water rich phase. On the other hand, the resole resincontaining no fumed silica, i.e., Sample No. C, has a distinct waterrich phase laying on the top of the remainder of the resole resincomposition. Upon pouring the water rich phase into a graduatedcylinder, the amount of water is found to be 0.5 ml, i.e., about 0.5 g.

In this manner, by the method of this invention, a finely divided,water-absorbent powder is found to stabilize a phenolic resole resin.

In a like manner, four stabilized phenolic resole resin compositions,similar in all respects to Sample No. 1 except that each resincomposition also contains 0.09 weight percent based on the weight of theresole resin of one of the following basic materials: magnesium oxide,calcium oxide, calcium hydroxide and tridimethylaminomethylphenol, areprepared. After being stored for three months at 22° C. in anessentially air impermeable container, these four stabilized resins arefound to exhibit essentially no distinct water rich phase. In thismanner, it is shown that the basic materials have no adverse effects onthe stability of the stabilized resin composition.

EXAMPLE 2

To a high speed mixer is added 1,000 parts of a resole resin of thereaction product of a formaldehyde and phenol mixture at a molar ratioof 1.4 moles of formaldehyde to 1 mole of phenol. To the resole resin inthe mixer is added 41 parts of a flaked graphite (No. 635 Graphite), 25parts of a fumed silica having a number average particle size of 120 A,0.6 part of magnesium oxide (magnesia) and 0.4 part of a 25 weightpercent aqueous solution of di-isobutylene-maleic anhydride sodium salt.

The resole resin and the adjuncts are blended for about 2 minutes at aspeed of about 15,000 to 20,000 rpm. The resulting stabilized resoleresin is a thixotropic liquid having a creamy smooth appearance andviscosity of about 140,000 cps (HBT type Brookfield viscometer, TAspindle, heliopath, at 5 rpm). It is conveyed to a container for storageat ambient conditions. After three months of storage, the container isinspected, revealing a thixotropic liquid having no distinct waterlayer.

To the stabilized resin composition is added 107 parts of a catalystcomprising a mixture of 20 weight percent trichloroacetic acid and 80weight percent of benzene sulfonyl chloride. The catalyst is blended byhand into the resin composition.

The catalyzed resin composition is placed in airless spray equipment andsprayed on the surfaces of a holding tank. The surfaces are sand blastedsteel which have been primed with a vinyl ester resin sold as DERAKANE®by The Dow Chemical Company. The resin coating is allowed to cure atambient conditions for about 24 hours. At this time the cured resincoating is a hard, solvent-resistant coating. Visual inspection showsthe coating to be free of pinholes and other imperfections.

The storage tank with the cured resin coating contains a mixture ofaluminum chloride, hydrochloric acid, ethylbenzene and water attemperatures of about 50°-60° C. After a period of 19 months there is nonoticeable degradation in the coating and no substantial loss ofadhesion between the coating and the DERAKANE® coated steel surfaces.

What is claimed is:
 1. A method of preparing a coating from a stabilizedphenolic resole resin composition of a phenolic resole resin and anamount of a finely divided, water absorbent powder having a numberaverage particle size of less than about 5,000 A sufficient to reducethe amount of a distinct, water rich phase formed in the phenolic resoleresin; said method comprising the steps of:(a) adding a catalytic amountof an acid to the stabilized resole resin composition; (b) applying thecatalyzed resole resin composition to a suitable substrate; and (c)subjecting the catalyzed resole resin composition to conditionssufficient to cure the resin on the substrate.
 2. The method of claim 1wherein the acid catalyst is employed in an amount from about 0.1 toabout 15 weight percent based on the weight of the resole resin and thecatalyzed resole resin composition is subjected to temperatures fromabout 20° to about 100° C.
 3. The method of claim 2 wherein the finelydivided powder is a fumed inorganic powder.
 4. The method of claim 3wherein the phenolic resole resin is the reaction product of phenol andformaldehyde or a formaldehyde generating material, the catalyst isemployed in an amount from about 0.2 to about 10 weight percent based onthe weight of the resole resin and the catalyzed resole resincomposition is subjected to temperatures from about 20° to about 100° C.to cure the resin.
 5. The method of claim 4 wherein the stabilizedresole resin composition comprises from about 0.5 to about 5 weightpercent of the fumed powder based on the weight of the phenolic resoleresin and the fumed inorganic powder is fumed silicon dioxide, fumedtitanium dioxide or fumed aluminum oxide having a number averageparticle size of less than about 400 A.
 6. The method of claim 5 whereinthe fumed inorganic powder is fumed silicon dioxide.
 7. The method ofclaim 1 wherein the acid catalyst is employed in conjunction with anorganic sulfonyl chloride.
 8. The method of claim 7 wherein the acidcatalyst is employed as a mixture of from about 5 to about 50 weightpercent of the acid and from about 95 to about 50 weight percent ofbenzene sulfonyl chloride, said weight percents being based on theamount of acid and sulfonyl chloride.